> "excess solar power from households and businesses spilled uncontrolled on to the system" ... Wow, that sounds like a great problem to have.
It's also a problem that has already been solved at the technology level.
Australia just needs an equivalent to California's updated "Rule 21" regulations for smart inverters, which came into force in 2019. These rules require inverters to support "remote control" management by utilities, so that their output can be throttled back in low-demand scenarios.
Rule 21 also specifies features like dynamic volt/VAR (dynamic reactive compensation), so inverters actively work to stabilise the grid in the event of voltage deviations, as well as ramping and "ride through" requirements to prevent large numbers of inverters tripping simultaneously during voltage/frequency deviations which could result in a cascading fault.